Generation of $\gamma$ photons with extremely large orbital angular momenta

TL;DR

This paper presents a quantum theory for generating vortex gamma photons with large orbital angular momentum via nonlinear Compton scattering, enabling new applications in physics by producing photons with adjustable OAM at moderate laser intensities.

Contribution

It develops a comprehensive quantum radiation model for vortex electrons interacting with lasers, revealing mechanisms for creating high-OAM gamma photons with specific properties.

Findings

Vortex gamma photons can carry OAM quantum numbers from tens to thousands.

Large topological charges in vortex electrons enable high-OAM gamma photon generation.

The theory predicts conditions for producing gamma photons with large OAM and coherence length.

Abstract

Vortex $\gamma$ photons, which carry large intrinsic orbital angular momenta (OAM), have significant applications in nuclear, atomic, hadron, particle and astro-physics, but their production remains unclear. In this work, we investigate the generation of such photons from nonlinear Compton scattering of circularly polarized monochromatic lasers on vortex electrons. We develop a quantum radiation theory for ultrarelativistic vortex electrons in lasers by using the harmonics expansion and spin eigenfunctions, which allows us to explore the kinematical characteristics, angular momentum transfer mechanisms, and formation conditions of vortex $\gamma$ photons. The multiphoton absorption of electrons enables the vortex $\gamma$ photons, with fixed polarizations and energies, to exist in mixed states comprised of multiple harmonics. Each harmonic represents a vortex eigenmode and has transverse momentum broadening due to transverse momenta of the vortex electrons. The large topological charges associated with vortex electrons offer the possibility for $\gamma$ photons to carry adjustable OAM quantum numbers from tens to thousands of units, even at moderate laser intensities. $\gamma$ photons with large OAM and transverse coherence length can assist in influencing quantum selection rules and extracting phase of the scattering amplitude in scattering processes.